Presta valve query

[Helpmefixmybike]

I'm borrowing a friend's bike for the summer; its an old Raleigh from the 1980s and it has presta valves. Presta valves are completely new to me. I've got a presta valve pump, so no probs there regarding adapters etc. I've watched YouTube tutorials about working presta valves. However the tires are proving very difficult to inflate. Once I stop pumping and try to remove the pump it deflates immediately back through the hand pump. I don't even have to depress the stumpy screw at the end to release air/break the seal to deflate, it does it on its own. Is this normal, or are the valves tired and in need of replacing? Or do I need a new pump, as that is about the same age? Is it possible to get presta valve tires inflated to a high standard, or is this difficulty quite typical?? Please help!

[Bill]

(06-02-2010, 06:44 PM)Helpmefixmybike Wrote:  I'm borrowing a friend's bike for the summer; its an old Raleigh from the 1980s and it has presta valves. Presta valves are completely new to me. I've got a presta valve pump, so no probs there regarding adapters etc. I've watched YouTube tutorials about working presta valves. However the tires are proving very difficult to inflate. Once I stop pumping and try to remove the pump it deflates immediately back through the hand pump. I don't even have to depress the stumpy screw at the end to release air/break the seal to deflate, it does it on its own. Is this normal, or are the valves tired and in need of replacing? Or do I need a new pump, as that is about the same age? Is it possible to get presta valve tires inflated to a high standard, or is this difficulty quite typical?? Please help!

I am not a pro at the presta valves but maybe this video will help you...

http://bikeride.com/presta-valve/

P.S. It may be a good idea to replace the pump if it is that old. Unless it has good ratio.

[j beede]

I only use a presta pump on the road for emergencies. In the garage I use a presta adapter with a standard Schroeder floor pump ($29 at performance). I find this setup to be more reliable and I can easily get 120 PSI in the tire with virtually no bleed off when I remove the pump. I cannot say the same for the presta pump.
...j

[DaveM]

If you find that the presta pump leaks a lot of air as you try to remove it, it may be that you have the pump pushed on too far. On a schraeder, the pump has to push the center pin down for air to flow, so the pump has to go on far enough to activate the valve. On presta, the air pressure opens the valve, the pump just has to go on far enough so that you get a good seal. If it's on too far, it pushes down the center pin and holds the valve open so as you release the seal, a lot of air can leak out. I'd try seeing if you can slide the pump less far on the valve body and still get a tight seal while you're pumping.

Presta absolutely can handle higher pressures which is one reason you see them on racing bikes. But because the tire volume is so small, even leaking a little air can lead to very low final pressure.

Like j beede, I've used pumps where it is easier to use an adapter. I think this is because the design of the pump doesn't let you get a good seal without going on so far that you force down the pin on the presta valve. Other pumps work great without an adapter.

That all said, the OP says that he doesn't "even have to depress the stumpy screw at the end to release air". If so, it sounds like the tubes are bad. Although that's pretty rare.